Smell is organic, and the smell is there even when the AC is off as it's caused by a gas leakage from the evaporator. The smell will condensate inside the dashboard and then it would get through the vents and into the cabin as soon as you turn the ventilation or the AC on.
Several minutes after turning vent or AC on, the smell would fades away and becomes unnoticeable, until the next journey, the process repeats itself again and again...
if you want to make sure your AC system has no gas leakage, you can ask the dealer to put pressurise it and monitor it for 24 hours or so, if the pressure drops, then it's most probably the evaporator.

That makes zero sense. Do you understand how an automotive AC system works?

What exactly is your "organic"? R134a? Yeah right. An evaporator or any joint could seep refrigerant, and it can have an odor at high concentrations, but if they were sniffing refrigerant, for one thing it wouldnt last long since it would be all gone quick, but if it were in a concentration to smell it, it would. One out faster and be more noticeable with the AC on since the system runs at a higher pressure than if it were off and just equilibrated thermally with the ambient.

Organic from some bacteria or mildew I will agree with. I get this sometimes in my 135i and my Saab. The basis of the evaporator closing with the HVAC system turning off is plausible for stink after the HVAC is turned back on (orpine when the car is turned off then started back up). But the situation here occurs when the AC only is turned off (air still flowing), which means it is going through the evaporator and ducting, just in a monster state, which for whatever reason creates the smell.

That makes zero sense. Do you understand how an automotive AC system works?

What exactly is your "organic"? R134a? Yeah right. An evaporator or any joint could seep refrigerant, and it can have an odor at high concentrations, but if they were sniffing refrigerant, for one thing it wouldnt last long since it would be all gone quick, but if it were in a concentration to smell it, it would. One out faster and be more noticeable with the AC on since the system runs at a higher pressure than if it were off and just equilibrated thermally with the ambient.

Organic from some bacteria or mildew I will agree with. I get this sometimes in my 135i and my Saab. The basis of the evaporator closing with the HVAC system turning off is plausible for stink after the HVAC is turned back on (orpine when the car is turned off then started back up). But the situation here occurs when the AC only is turned off (air still flowing), which means it is going through the evaporator and ducting, just in a monster state, which for whatever reason creates the smell.

Well, I'm just describing what happened to my car, organic or not, the smell was there, with AC or just fan... And after replacing the evaporator, the smell is gone. Coincidence ? Who knows.